1. Field of the Invention
The present invention relates to a fuel cell comprising a membrane electrode assembly having a solid polymer electrolyte membrane, an anode side gas diffusion electrode disposed at one side of the solid polymer electrolyte membrane, and a cathode side gas diffusion electrode disposed at the other side of the solid polymer electrolyte membrane, and a pair of separators holding the membrane electrode assembly; and to a method for producing the same: In particular, the present invention relates to a fuel cell in which the membrane electrode assembly can be reliably sealed between the separators, and to a method for producing the same.
Further, the present invention relates to a fuel cell in which the peripheries of openings for fuel gas, oxidant gas, and coolant is reliably sealed, and to a method for producing the same.
Further, the present invention relates to a fuel cell stack whose fuel cell units can be easily replaced.
2. Description of the Related Art
In conventional fuel cells, the membrane electrode assembly comprises a solid polymer electrolyte membrane, and an anode side diffusion electrode and a cathode side diffusion electrode which are disposed at both sides of the membrane. The membrane electrode assembly is held by a pair of separators. By supplying fuel gas (for example, hydrogen gas) onto a reaction surface of the anode side diffusion electrode, the hydrogen gas becomes ionized, and moves toward the cathode side diffusion electrode through the solid polymer electrolyte membrane. The electrons produced in this process are extracted to an external circuit, and are utilized as electric energy of a direct current. Since oxidant gas (for example, air which contains oxygen) is supplied to the cathode electrode, water is generated by the reaction of the hydrogen ions, the electrons, and the oxygen.
An example is explained with reference to FIG. 17. In FIG. 17, reference numeral 1 denotes the solid polymer electrolyte membrane. A fuel cell 4 is assembled such that the solid polymer electrolyte membrane 1 is held between gas diffusion electrodes (an anode side diffusion electrode and a cathode side diffusion electrode) 2 and 3. Sheet-type gaskets 5 which have openings corresponding to the reaction faces of the fuel cell 4 are provided at both sides of the fuel cell 4. While the gaskets 5 cover the edges of the fuel cell 4 and press the edges of the fuel cell 4 using outer pressers, the fuel cell 4 is held between separators 7 (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 6-325777).
In the above conventional fuel cell, the gaskets 5 separate the spaces between the separators 7 and the gas diffusion electrodes 2 and 3 from the outside. Therefore, this fuel cell advantageously prevents the leakage of the fuel gas and the oxidant gas, and prevents the mixing of those gases, to thereby achieve efficient electric power generation. Variations in the thickness of the separators 7 and 8 and the gas diffusion electrodes 2 and 3 are unavoidable. Therefore, when the gaskets 5 which have varying thicknesses are combined with the separators 7 and the gas diffusion electrodes 2 and 3, the reaction force produced by the gaskets is not uniform. Thus, there is the problem that the sealing between the separators 7 and the gas diffusion electrodes 2 and 3 is not uniform.
Further, the fuel cell has an internal manifold for supplying fuel gas, oxidant gas, and coolant to the anode side diffusion electrode and the cathode side diffusion electrode. The internal manifold has a number of openings through the separators.
An example of the conventional technique will be explained with reference to FIG. 32. Reference numeral 201 denotes a solid polymer electrolyte membrane. The fuel cell 204 is assembled such that the solid polymer electrolyte membrane 201 is held by gas diffusion electrodes (an anode side diffusion electrode and a cathode side diffusion electrode) 202 and 203. The fuel cell 204 is held between separators 205 and 205.
Openings 206 which constitute the internal manifold are formed in the peripheries of the separators 205 holding the fuel cell 204. The oxidant gas, or the fuel gas supplied from the openings 206 reaches the reaction surfaces of the respective fuel cells 204.
To seal the peripheries of the openings 206, a gasket 207 is inserted between the separators 205 and makes contact with the peripheries of the openings 206 (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 6-96783, and U.S. Pat. No. 4,510,213).
The above-mentioned fuel cell has problems in that the surface pressure of the gasket 207 varies in the peripheries of the openings of the separators 205, and in that a partial bending stress acts in the peripheries of the openings.
Another conventional fuel cell will be explained with reference to FIG. 47. In FIG. 47, reference numeral 301 denotes a solid polymer electrolyte membrane 301. The fuel cell 304 is assembled such that the solid polymer electrolyte membrane 301 is held by gas diffusion electrodes (an anode side diffusion electrode and a cathode diffusion electrode) 302 and 303. The fuel cells 304 are held via carbon plates 305, which are disposed in the peripheries thereof, by separators 306 and 306. The fuel cell units are assembled such that the separators 306 are attached to the fuel cells 304 by two-side adhesive agent sheet 307, and the fuel cell units are stacked to produce the fuel cell stack (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 9-289029).
That is, the fuel cells 304 and the separators 306 are bound by the two-side adhesive agent sheet 307, and the fuel cell units are thus assembled. Then, the fuel cell units are stacked. However, there is the problem in that, when replacing either the solid polymer electrolyte membrane 301 or the separators 306, the two-sided adhesive agent sheet 307 must be separated, and this takes much labor.
Further, when the two-sided adhesive agent sheet 307 is separated, components other than the replaced component may be deformed.
It is therefore an object of the present invention to provide a fuel cell which can improve the seal between the membrane electrode assembly and the separators, and a method for producing the same.
In the first aspect of the present invention, the fuel cell comprises: a membrane electrode assembly (12) having a solid polymer electrolyte membrane (18), an anode side gas diffusion electrode (an anode electrode 22, and a second gas diffusion layer 26) disposed at one side of the solid polymer electrolyte membrane, and a cathode side gas diffusion electrode (a cathode electrode 20, and a first gas diffusion layer 24) disposed at the other side of the solid polymer electrolyte membrane; a pair of separators (14 and 16) which hold the membrane electrode assembly; a projecting portion (18a) which extends from the solid polymer electrolyte membrane and which projects from the peripheries of the anode side diffusion electrode and the cathode side diffusion electrode; and a seal, provided onto the separators, which was a liquid sealant (S) at the time of application. The sealant makes contact with the projecting portion while the membrane electrode assembly is disposed between the separators.
In the second aspect of the present invention, the seal is provided in grooves (28) formed in the separator.
According to the first and second aspects of the present invention, the liquid sealant (which means liquid or gel sealant) is directly in contact with the projecting portion provided at the periphery of the solid polymer electrolyte membrane, is pressed between the solid polymer electrolyte membrane and the separators, fitting the varying sizes of the seal sections, and maintains gas-tightness between the solid polymer electrolyte membrane and the separators. Therefore, the reaction force produced by the seal is uniform throughout the periphery between the separators and the membrane electrode assembly, thereby making the sealing uniform. The manufacturing sizes of the separators and the membrane electrode assembly in the directions of thickness need not be accurately controlled. Management of the accuracy in size is easy, and manufacturing costs can be reduced.
Further, the liquid sealant compensates for variation in the sizes of the seal sections between the separators and the projecting portion of the solid polymer electrolyte membrane, and therefore prevents partial forces from acting on the separators. Therefore, the separators can be thin, the fuel cell can be light, and the size of the fuel cell can be reduced. The fuel cell of the present invention is suitable for a vehicle in which the space for the fuel cell is limited, and in which it is desirable for the separators to be as thin as possible.
In the third aspect of the present invention, if the diameter of the applied liquid sealant is C, the width e of the projecting portion is equal to or greater than {fraction (3/2)}xc3x97C.
According to the third aspect of the present invention, in addition to the above effects, the width of the projecting portion of the solid polymer electrolyte membrane can be at a minimum while achieving a reliable sealing. That is, the projecting portion which does not contribute to the reaction of gases can be minimized while improving the sealing.
In the fourth aspect of the present invention, the a diameter of the applied liquid sealant is equal to or greater than 0.9 mm.
According to the fourth aspect of the present invention, the width of the contact of the liquid sealant is suitable when manufacturing the fuel cell, and the manufacturing process can be simplified.
It is therefore an object of the present invention to provide a fuel cell in which it is possible to improve the sealing in the peripheries of the opening of the separator, and a method for producing the same.
In the fifth aspect of the present invention, the fuel cell comprises: a membrane electrode assembly (12) having a solid polymer electrolyte membrane (18), an anode side diffusion electrode (an anode electrode 22, and a second diffusion layer 26) disposed at one side of the solid polymer electrolyte membrane, and a cathode side diffusion electrode (a cathode electrode 20, and the first diffusion layer 24) disposed at the other side of the solid polymer electrolyte membrane; a pair of separators (14 and 16) which hold the membrane electrode assembly, each of the separators having an opening (36a, 38a, 40a, 40b, 36b, or 38b) for supplying or discharging one of a fuel gas, an oxidant gas, and a coolant to or from the membrane electrode assembly; a seal, which was liquid sealant (SA1) at the time of application, which encloses the openings of the separators, the seal on one separator making contact with the seal on the other separator to seal the periphery of the opening.
In the sixth aspect of the present invention, the separators have grooves (30) which enclose the openings, and the seal is provided in the grooves.
According to the fifth and six aspects of the present invention, the seal is directly in contact with the projecting portion provided at the periphery of the solid polymer electrolyte membrane 18, is pressed between the separators, fitting the varying sizes of the seal sections, and maintains gas-tightness in the peripheries of the openings. Therefore, the reaction force produced by the seal is uniform throughout the peripheries of the openings, thereby making the sealing uniform. The manufacturing sizes of the separators in the direction of thickness need not be accurately controlled. Management of the accuracy in size is easy, and manufacturing costs can be reduced.
In the seventh aspect of the present invention, the fuel cell comprises: a membrane electrode assembly having a solid polymer electrolyte membrane, an anode side diffusion electrode disposed at one side of the solid polymer electrolyte membrane, and a cathode side diffusion electrode disposed at the other side of the solid polymer electrolyte membrane; a pair of separators which hold the membrane electrode assembly, each of the separators having an opening for supplying or discharging one of a fuel gas, an oxidant gas, and a coolant to or from the membrane electrode assembly; and a seal, which was liquid sealant at the time of application, which encloses the openings of one of the separators, and which makes contact with the other separator to seal the periphery of the opening.
In the eighth aspect of the present invention, one of the separators has a groove which encloses the opening, and the seal is provided in the grooves.
The seventh and eighth aspects of the present invention achieves the same effects as those of the fifth and six aspects, and reduces the manufacturing costs because the liquid sealant and the groove are provided only on one of the separators.
It is therefore an object of the present invention to provide a fuel cell stack whose fuel cell units can be easily replaced.
In the ninth aspect of the present invention, the fuel cell stack (N) has a plurality of fuel cell units (10). Each of the fuel cell units (10) comprises: a membrane electrode assembly (12) having a solid polymer electrolyte membrane (18), an anode side diffusion electrode (an anode electrode 22, and a second diffusion layer 26) disposed at one side of the solid polymer electrolyte membrane, and a cathode side diffusion electrode (cathode electrode 20, and a first diffusion layer 24) disposed at the other side of the solid polymer electrolyte membrane; a pair of separators (14 and 16) which hold the membrane electrode assembly; an adhesive seal (SB), provided between the separators, which was liquid sealant at the time of application; and non-adhesive seal (SB1, or KS1) provided between the separator of one fuel cell unit and the separator of the other fuel cell unit.
In the tenth aspect of the present invention, the non-adhesive seal was liquid sealant at the time of application.
In the eleventh aspect of the present invention, the non-adhesive seal was solid sealant at the time of application.
According to the ninth to eleventh aspects of the present invention, the non-adhesive sealant is provided between the separators in the stacked fuel cell units. therefore, when replacing one of the fuel cell units, each of the fuel cell units can be easily disassembled and reassembled. Thus, rebuildability is improved. Because the adhesive seal binds the separators holding the fuel cell, the membrane electrode assembly is prevented from accidentally being separated when disassembling or reassembling the fuel cell stack. Further, the diffusion electrodes and the separators are prevented from being accidentally separated.